1. Field of the Invention
The present invention relates to a process for producing a granular (or powdered) detergent composition having a high bulk density by disintegrating a solid detergent composition.
2. Description of the Related Art
Granular detergent compositions have heretofore been produced mainly by spray drying. In the spray drying process, detergent ingredients such as surfactants and builders are mixed with water to form a slurry having a water content of 35% to 50% by weight. The slurry thus obtained is sprayed, after heating, into a heated space in a spray dryer to form bead type hollow particles having a water content of 5% to 10% by weight and a bulk density of approximately 0.3 g/cc.
The spray drying is advantageous in that a hollow granular detergent having an excellent solubility can be obtained. However, since 30% to 40% by weight of water must be removed in the drying step, an extremely large heat energy is disadvantageously consumed. Also, since large scale production equipment is required, a large initial investment is necessary. Furthermore, since the granules obtained by the spray drying have a low bulk density, the packaging volume becomes disadvantageously large. Furthermore, since the granules obtained by spray drying have large irregularities on the surface of the granules, the flowability and appearance thereof are poor.
In addition, when granular detergents are prepared by the spray drying, the production of detergent compositions having a high surfactant content and the use of heat susceptible substances such as nonionic surfactants is limited. The spray drying is also disadvantageous in that, since powder dust is likely to be generated due to the finely divided powder particles, completely dust-free products are difficult to obtain.
Various attempts have been made to produce granular detergent compositions by methods other than spray drying. For instance, Japanese Examined Patent Publication (Kokoku) Nos. 46-7586 and 55-49535 and Japanese Unexamined Patent Publication (Kokai) No. 49-74703 disclose the use of substances having water of crystallization or substances capable of readily melting upon heating as a starting material for the production of granular detergent compositions. According to there methods, the above-mentioned substances are subjected to heat treatment to cause the discharge of water of crystallization therefrom or the melting thereof. These substances work as a binder to allow several to several dozen powder particles to be agglomerated and granulated. However, these methods still have problems from the practical point of view in that the particle size distributions of the resultant powder particles are wide or the water solubility thereof is poor.
Furthermore, Japanese Unexamined Patent Publication (Kokai) NOs. 60-72998 and 60-72999 recently disclose a method for neutralizing a mixture of alkylbenzene sulfonic acids and alkylsulfuric acid esters with sodium carbonate and a method for neutralizing sulfonates or sulfate with sodium carbonate, followed by disintegrating, after cooling to 40.degree. C. or less, the neutralized product together with zeolite and the other detergent ingredients. However, these methods still have problems from the practical point of view in that the dispersibility and solubility of the resultant composition in cold water are poor and powder dust is remarkably generated from the products due to the post-addition of a large amount of the powdered zeolite. Thus, the commercial value is poor.
Still further, when certain surfactants such as olefin sulfonates are formulated into granular detergent compositions having a high bulk density, the solubility thereof in water is decreased and, therefore, a sufficient detergency cannot be obtained in a conventional washing time and the detergent powder is sometimes deposited on clothing after washing.
Furthermore, in order to improve the water solubility of a granular detergent composition having a high bulk density, a method is used of adding a foaming substance to the granular detergent composition. However, this method involves a problem in that, since the substance having no effects on the detergency is additionally included in the detergent composition, the amount of the composition used in each washing and, therefore, the washing cost are increased.
Pan granulators are also conventionally used in the production of granules having a larger bulk density. According to this granulation method, powder is introduced into a rotating pan and water drops are, then, dropped to form nuclei, followed by growing spherical granules. However, this method is disadvantageous in that not only is the production time long, but also the growing of the nuclei caused by the water drops is remarkably fluctuated so that the size of the spherical granules produced becomes remarkably nonuniform.
Japanese Examined Patent Publication (Kokoku) No. 58-44120 discloses the use of a marumerizer as a post granulation apparatus for granular detergent composition. The marumerizer is disclosed in Japanese Examined Patent Publication (Kokoku) NO. 41-563 and is an apparatus for adjusting particle sizes of granules or sphering granules. This apparatus is composed of a cylinder and a disc provided at the bottom of the cylinder . The disc is rotated at a high speed and the granular substances are rotated thereon during the operation. However, the use of the marumerizer involves problems in that a driving device is required for rotating the disc, the maintenance is troublesome since granulating substances are clogged in a clearance between the cylinder wall and the disc, and since a scaling-up of the apparatus is difficult, the treatment capacity is limited and a continuous operation is difficult.